1. Field of the Invention
This invention relates generally to a method and apparatus for controlling an internal combustion engine, and more particularly to a microprocessor-based electronic engine control system having a memory preprogrammed with various control laws and control schedules responsive to one or more sensed engine-operating parameters for generating signals for controlling fuel injection, ignition timing, EGR control, or the like.
2. Statement of the Prior Art
Many of the patents of the prior art recognize the need for employing the enhanced accuracy of digital control systems for more accurately controlling one or more functions of an internal combustion engine.
U.S. Pat. No. 3,969,614 which issued to David F. Moyer, et al on July 13, 1976 is typical of such systems as are U.S. Pat. No. 3,835,819 which issued to Robert L. Anderson, Jr. on Sept. 17, 1974; U.S. Pat. No. 3,904,856 which issued to Louis Monptit On Sept. 9, 1975; and U.S. Pat. No. 3,906,207 which issued to Jean-Pierre Rivere, et al on Sept. 16, 1975. All of these Patents represent a break-away from the purely analog control systems of the past, but neither the accuracy, reliability, or number of functions controlled is sufficient to meet present day requirements.
Future internal combustion engines will require that emissions be tightly controlled due to ever-increasing governmental regulations, while fuel consumption is minimized and drivability improved over the entire operating range of the engine. None of the systems of the prior art provide a method and apparatus for controlling the operation of an internal combustion engine over even a portion of its operating range with sufficient accuracy to attain minimal emissions and minimal fuel consumption along with improved drivability.
Many of the systems of the prior art have attempted to utilize feedback from oxygen sensors located in the exhaust system for controlling various engine-operating conditions. These attempts were met with little success due to the relative unreliability of the present day oxygen sensors and the inability of such sensors to produce signals of significant magnitude on either side of stiochiometric air-fuel ratios.
The application of the present invention permits the use of an oxygen sensor feedback system for control purposes by ensuring that the oxygen sensor signals are properly conditioned and for testing sensor temperature and generating an inhibit signal to inform the computing system that a low temperature condition exist and hence that the possibility of unreliable sensor readings exists.